Cyclic olefins are subjected to ring-opening metathesis polymerization to produce thermoplastic and thermoset polymers having physical properties which make them suitable for structural and electronic applications, such as molded plastic items and electrical laminates. Such polymerizations are commonly carried out in reaction injection molding (RIM) processes, in which a metathesis catalyst and a cyclic olefin monomer are charged to a heated mold, and polymerization of the monomer and forming of the polymer into the desired shape are carried out simultaneously in the mold.
In such RIM processes, it is important that the polymerization reaction occur rapidly and with as complete incorporation of the charged monomers as possible. For example, the presence of unreacted monomers in molded polydicyclopentadiene has been found to result in a molded part with an unpleasant odor, and less than optimum physical properties. Finding a RIM process that reacts in as short a cycle time as possible and at mold temperatures at or near room temperature is economically desirable. Further, it is desirable in such a system to have catalyst systems which are thermally stable and resistant to reaction with oxygen and water.
For most cyclic olefin metathesis catalyst systems, the presence of reactive materials such as water and oxygen should be avoided because they foul the polymerization process. As a result, it is usually necessary to thoroughly dry the cyclic olefin monomers prior to contact with the polymerization catalyst, and to conduct the polymerization in an inert environment.
A tungsten(VI) oxo alkylidene complex with an aluminum chloride co-catalyst is disclosed in an article by J. A. Boncella et al., J. Am. Chem. Soc., 113, 7066-7068 (1991) as an air and moisture-stable ring opening metathesis catalyst system. However, alkylidene or alkylidyne complexes, e.g. W.dbd.CR or W.dbd.CR, are generally difficult to manufacture and expensive. Therefore, it is desirable to produce a simpler and less expensive, air and moisture-stable ring opening metathesis catalyst system.
It is therefore an object of the present invention to provide an improved air and moisture-stable ring opening metathesis catalyst system.